1. Field of the Invention
The present invention relates to a secondary battery, and more particularly to a secondary battery having a structure allowing an electrode tap to be welded to an interior end of an electrode terminal and/or an interior-facing surface of a terminal plate.
2. Description of the Related Art
As is well-known in the art, a secondary battery is a rechargeable battery whereas a primary battery is not rechargeable. Secondary batteries are used in the field of high-tech electronic equipment like cellular phones, notebook computers and camcorders. The operating voltage of a lithium secondary battery is 3.6 volts, about three times larger than a nickel-cadmium battery or a nickel-hydrogen battery often used to power electronic equipment. Thus, lithium secondary batteries have become widely used because of their high energy density per unit weight.
Conventional lithium secondary batteries use lithium oxides as an active positive polarity substance and use carbon materials as an active negative polarity substance. Lithium secondary batteries are manufactured in various shapes such as a cylindrical shape, a cone shape, a pouch shape, and others.
A conventional secondary battery usually includes a can, an electrode assembly housed in the can and a cap assembly coupled with the can. The cap assembly includes a cap plate coupled with the upper part of the can, an electrode terminal installed through a terminal hole and having a gasket for insulation from the cap plate, an insulating plate installed on an interior surface of the cap plate, and a terminal plate installed on an interior-facing surface of the insulating plate to contact the electrode terminal. One electrode of the electrode assembly is electrically connected to the electrode terminal through an electrode tap and the terminal plate, and the other electrode is electrically connected to the cap plate or the can through an electrode tap connected thereto.
To assemble the cap assembly, the electrode terminal is rotated and inserted into a terminal hole on the cap plate and holes on the insulating plate and the terminal plate. The end of the electrode terminal inserted into the terminal plate is compressed.
However, the conventional cap assembly has certain drawbacks. The interior end of the electrode terminal, which is inserted and compressed in the hole formed on the terminal plate, protrudes further into the secondary battery than the neighboring interior surface of the terminal plate, thus making it difficult to weld or attach the electrode tap on the interior end of the electrode terminal directly.
As such, it is necessary to extend one side of the terminal plate to weld it to the electrode tap. It is not possible to extend both sides of the terminal plate since the electrode taps must have opposite polarities. As a result, a terminal plate and an insulating plate that are asymmetrical about the electrode terminal are used.
Accordingly, when the electrode terminal is rotated and inserted, the structure when the structure fixing the insulating plate may also rotate since its resistance against rotation is weak. Therefore, a short circuit may occur between the cap plate and the terminal plate.
Also, since the electrode tap is not directly welded to the interior end of the electrode terminal but rather is welded to one side of the terminal plate, the path through which the current produced from the battery portion flows is longer and the electric resistance increases.